The present invention relates to a drainage structure in a polishing plant.
In the manufacture of semiconductor wafers, a polishing apparatus has been used for polishing a semiconductor wafer so as to enable a surface of the semiconductor wafer to be made flat with a mirror-surface finish. Generally, a polishing apparatus is used in combination with a cleaning apparatus for cleaning and drying semiconductor wafers after polishing. In a conventional polishing plant comprising a polishing apparatus and a cleaning apparatus, a number of drainage pipes are employed to discharge various liquids which have been used in various devices in the polishing and cleaning apparatuses, and these drainage pipes are connected to a single pipe. Therefore, in the above-mentioned conventional polishing plant, the liquids which have been used in various devices in the polishing and cleaning apparatuses are individually discharged as waste liquids through the drainage pipes from those devices, collected into the single pipe, and finally discharged from the polishing plant through a single drainage pipe line.
In the above-mentioned conventional polishing plant in which various waste liquids are finally discharged from the polishing plant through a single drainage pipe line, it is impossible to perform different treatments of waste liquids depending on the type of waste liquid to be treated (e.g., the concentration of impurities and the type of chemicals). The waste liquids finally discharged from the polishing plant are supplied to a solid matter-treating apparatus, in which solid matter in the waste liquids is removed, and are transferred to a factory drainage line as an industrial waste liquid.
Therefore, in a conventional polishing plant, even a waste liquid which is not seriously contaminated or does not contain solid matter is subjected to the same treatment as performed with respect to a waste liquid which is seriously contaminated or contains solid matter, so that not only does a waste liquid-treating plant inevitably become large, but costs of operation for treating waste liquids also become high. Further, in a conventional polishing plant, it is impossible to reuse a reusable waste liquid which is not seriously contaminated, because various types of waste liquids are mixed with the reusable waste liquid. In addition, there is a danger such that a chemical reaction may occur when various chemicals used in the polishing and cleaning apparatuses are mixed.